This invention relates to an improved embodiment of a laser instrumentation device described and claimed by this applicant, in the U.S. Pat. No. 3,786,907, and an earlier patent related to the same instrumentation system, U.S. Pat. No. 3,464,534. Both of these patents describe and claim semiconductor diode lasers as sources of laser radiation. However, U.S. Pat. No. 3,786,907 specifically discloses and claims a semiconductor diode-pumped laser generator for application in various industrial processes, more particularly in a laser eraser for correction of type-written errors. However the main point in this application resides in the use of new techniques and elements for generating laser radiation using newly-developed semiconductor diodes, such as light-emitting diodes or laser diodes. Both of these diodes are capable of producing spectral wavelengths compatible with the solid-state laser rods. However. the laser diode possesses the property of higher intensity of radiation and is more efficient in irradiating any solid-state laser rod and producing therefrom a laser-beam radiation of high performance characteristics.
The present invention further improves on said device shown in U.S. Pat. No. 3,786,907, and demonstrates that by frequency-doubling or Q-switching the laser diode's radiation or by using both the frequency-doubling and the Q-switching techniques a laser radiation beam is produced which has improved spectral and optical characteristics.
Conventional laser-generating systems employ inert-gas arc lamps, known as flashlamps, tungsten-filament lamps, and the like to illuminate (pump) the solid-state laser rod to generate laser radiation therefrom. The most common source of continuous pumping of laser radiation from a laser rod, such as a neodymium-doped yttrium-aluminum-garnet host (Nd-YAG), is the tungsten-filament halogen lamp. Another optical-pump source is the krypton arc lamp. The pumping lamp emits a blackbody-type radiation, whose efficiency in pumping a laser radiation from the solid-state rod, such as a ruby rod or a Nd-YAG rod, is between 5 to 6 percent. The light intensity from such a lamp heats it to a very high temperature. Therefore, most of the energy produced by the lamp is dissipated as thermal energy, which contributes to the heating of the laser-generating system, reducing its efficiency of emission. Consequently, cooling of the laser-generating system is necessary, using a cumbersome equipment of compressed air or water circulating through the laser-generating head. The service life of the lamp is short, typically 300 to 400 hours. These characteristics of the pumping lamp make the laser system bulky and costly to produce.
The efficiency of laser production of such an optical pumping lamp is also very low. For instance, for each 1000 watts of input power to the pumping lamp only about 25 watts of laser power is typically produced. This is an efficiency of about 2 percent, which is considered satisfactory at present because of the lack of other commercial means to produce greater efficiency of laser production. Furthermore, since the laser rod is heated by the thermal energy dissipated from the pumping light source, the efficiency of laser production of the rod also decreases, and its output becomes about 0.5 percent that of input. Accordingly, the present solid-state laser production techniques are too wasteful in energy utilization. For this reason, the laser systems are too costly for employment in many technical communities.
While the applicant's patent, U.S. Pat. No. 3,786,907, represents a new and basic principle of laser generation, by the use of a laser diode to pump a laser rod, such as Nd-YAG, ruby. erbium-YAG, alexandrite, or the like, the present application contains the same basic principle with improved design of construction using new elements to enhance additional advantages and efficiency to the laser system. As a matter of fact, the present disclosure fortifies the original basic system of the applicant's invention by the use of state-of-the-art laser-producing elements, fewer parts, low-cost materials, compactness in size, and more efficient laser pumping semiconductor laser diodes.
A typical laser diode for pumping laser rods is gallium arsenide (GaAs), which emits typically at about 8000 angstroms, with its hybrid from gallium-aluminum-arsenide (GaAlAs) emitting at 7500 to 9050 angstroms, and indium-gallium-arsenic-phosphide (InGaAsP) emitting at 11,000 to 16,000 angstroms in the infrared. Any of these laser diodes and their derivatives, such as for one gallium-indium-aluminum-arsenide (GaInAlAs) can be utilized in the present species of the applicant's invention, since each of these diodes has specific advatages, as will be presently indicated by reference to the drawings.
In the present invention, an array of any selected type of the laser diodes referenced above can be used. The diode offers a conversion efficiency of 25 percent and over, in some cases. This means that a 10-watts of input power can produce about 2.5 watts of laser radiation from the laser rod. An additional advantage of the diode laser over the flashlamp (tungsten-arc lamp, for instance) is that the radiation from the diode can be collimated and focused on the laser rod axially, matching with the TEM.sub.oo mode operation of the rod. TEM.sub.oo operation is the fundamental performance format of a laser element and is derived from the phrase "transverse electromagnetic mode", which mode simulates a Gaussian operational format, a most efficient performance mode of the laser system.
Since the semiconductor laser diode pumping of the laser rod possesses high effiency of radiation, the thermal problems are alleviated and consequent cooling operations, as necessary in other types of optical pumping methods, are not necessary. Thus, the cost of construction and operation of the laser system is reduced. Thermal birefringence effects and possible thermal focusing problems are also eliminated in diode pumping. One of the most important characteristics of the laser diode is the capability of being modulated easily at high speeds with high amplitude stabilization that is imparted to the laser rod by the diode performance.
By focusing the diode array radiation with a converging lens on the optical aperture of an optical fiber, the high energy from the diode array can be transferred through the fiber cable to a remotely-located laser rod, such as that shown in FIG. 2 of the drawing of the invention. This type of laser embodiment can enhance the reduction in the size of the laserhead; furthermore, a heatsink can be applied to the laserhead to cool it when necessary. The system then can be made small and simple in construction. Q-switching modelocking, tuning, and frequency-doubling design problems also become simplified and less costly, as shown in the present drawings.